In numerous applications, there is a need to measure precisely the location or position of an object. For example, many manufacturing processes require precise positioning of a moving stage or object. Several techniques for determining the position of a moving object have been developed. Some of these techniques are discussed below.
One method of determining the position of the moving stage involves optical encoding. In certain known optical encoding architectures, light from a light source is incident on a target pattern on the object. An optical sensor captures an image of the target pattern and from this image, the position of the object is determined.
Unfortunately, known optical encoders are comparatively large, which limits their implementation in certain settings. Moreover, thermal expansion in these comparatively large optical encoders can cause greater measurement error than the dimension being measured. Additionally, in many measurement environments it is useful to prevent contamination of the optical encoder due to ambient elements (e.g., dust and dirt) by enclosing the encoder in a suitable housing. As will be appreciated, the addition of the housing further increases the size of the encoder.
In addition to size-related drawbacks, many known two-dimensional optical encoders are limited by comparatively slow computational speeds. For example, in certain optical encoders the location of the object in each dimension must determined sequentially. As will be appreciated, this reduces the processing speed of measurement data. In many settings, comparatively slow processing speeds are a hindrance.
There is a need, therefore, for a system architecture for an optical encoder that overcomes at least the shortcoming of known optical encoders discussed above.